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Abstract:

The present application relates to a circular saw power tool having a
housing, a motor in the housing, a circular saw blade driven to rotate by
the motor, and a base plate that supports the housing and contacts the
surface of the workpiece to be cut. The housing is connected pivotably to
the base plate around a pivotal axis that is parallel to the rotation
axis, and the base plate has a slot for the circular saw blade to extend
below the base plate. The power tool has a first cutting mode that
provides cutting for a predetermined depth and a second cutting mode that
provides vertical cutting in a limited area, as well as a switching
device for switching between the first and second cutting modes. As a
result, the present application is able to integrate two different
cutting functions into a single power tool to increase work efficiency.

Claims:

1. A power tool comprising: a housing, a motor in the housing, a circular
saw blade driven to rotate by the motor and having a rotation axis, and a
base plate that supports the housing and contacts the surface of the
workpiece to be cut, wherein the housing is connected pivotably to the
base plate around a pivotal axis that is parallel to the rotation axis,
and the base plate has an elongated slot to allow the circular saw blade
to protrude below the base plate and a first depth adjustment mechanism
for adjusting the distance that the circular saw blade protrudes below
the base plate, the first depth adjustment mechanism comprising a depth
guide member connected to the base plate and having a first elongated
track thereon, and a clamp member for fixing the housing at a
predetermined position with regard to the base plate, wherein the power
tool also comprises an insert-type device that enables the circular saw
blade to cut vertically.

2. The power tool according to claim 1, wherein the insert-type device is
mounted on one of the base plate and the housing.

3. The power tool according to claim 1, wherein the power tool also
comprises a clutch device.

4. The power tool according to claim 3, wherein the clutch device has a
first clutch member and a second clutch member that mate with each other.

5. The power tool according to claim 4, wherein the first clutch member
is arranged on one of the base plate and the housing, and the second
clutch member is arranged on the insert-type device.

6. The power tool according to claim 4, wherein the power tool also
comprises a locking device for locking the first clutch member and the
second clutch member fixedly together when the first clutch member is
aligned with the second clutch member.

7. The power tool according to claim 4, wherein the power tool also
comprises an elastic member arranged between the second clutch member and
the insert-type device.

8. The power tool according to claim 1, wherein the power tool also
comprises a second depth adjustment mechanism that may adjust the area of
the vertical cutting of the circular saw blade.

9. The power tool according to claim 8, wherein the second depth
adjustment mechanism comprises a second track arranged on the depth guide
member, a backstop member slidable in the second track, and an operating
handle for operation by a user to fix the backstop member into the second
track.

10. The power tool according to claim 9, wherein the first track and the
second track have a common center.

11. A power tool comprising: a housing, a motor in the housing, a
circular saw blade driven to rotate by the motor and having a rotation
axis, and a base plate that supports the housing and contacts the surface
of the workpiece to be cut, wherein the housing is connected pivotably to
the base plate around a pivotal axis that is parallel to the rotation
axis, and the base plate has an elongated slot for the circular saw blade
protruding to below the base plate, wherein the power tool has a first
cutting mode that may implement the cutting in the predetermined depth
and a second cutting mode that may implement the vertical cutting in a
limited area, as well as an insert-type device that enables the circular
saw blade to cut vertically, the insert-type device having an elastic
member, wherein the elastic force of the elastic member is only present
when the power tool is in the second cutting mode.

12. The power tool according to claim 11, wherein the power tool also
comprises a movable guard which may be opened automatically under the
action of the linkage mechanism when the power tool is in the second
cutting mode.

13. The power tool according to claim 11, wherein the power tool also
comprises a switching device for switching between the first cutting mode
and the second cutting mode.

14. The power tool according to claim 13, wherein the switching device is
a clutch device.

15. A power tool comprising: a housing, a motor in the housing, a
circular saw blade driven to rotate by the motor and having a rotation
axis, and a base plate that supports the housing and works on the surface
of the workpiece to be cut, wherein the housing is connected pivotably to
the base plate around a pivotal axis that is parallel to the rotation
axis, and the base plate has an elongated slot for the circular saw blade
protruding to below the base plate, a first depth adjustment mechanism
for adjusting the distance that the circular saw blade protrudes below
the base plate, a second depth adjustment mechanism for adjusting the
area of the vertical cutting of the circular saw blade, and a depth guide
member connected to the base plate and having at least one track thereon,
wherein the power tool also comprises an insert-type device that enables
the circular saw blade to cut vertically and an elastic member.

16. The power tool according to claim 15, wherein the insert-type device
is mounted on one of the base plate and the housing.

17. The power tool according to claim 15, wherein the power tool also
comprises a clutch device.

18. The power tool according to claim 17, wherein the clutch device has a
first clutch member and a second clutch member that mate with each other.

19. The power tool according to claim 18, wherein the first clutch member
is arranged on one of the base plate and the housing, and the second
clutch member is arranged on the insert-type device.

20. The power tool according to claim 19, wherein the power tool also
comprises a locking device that locks the first clutch member and the
second clutch member fixedly together when the first clutch member is
aligned with the second clutch member.

21. The power tool according to claim 20, wherein the elastic member is
arranged between the second clutch member and the insert-type device.

22. The power tool according to anyone of claims 15, wherein the depth
guide device has a first track and a second track.

23. The power tool according to claim 22, wherein the second depth
adjustment mechanism also has a backstop member slidable in the second
track and an operating handle for operation by a user to fix the backstop
member into the second track.

24. The power tool according to claim 23, wherein the first track and the
second track have a common center.

[0003] The invention relates to a power tool, more particularly to a
hand-held power tool having a circular saw blade.

BACKGROUND OF THE INVENTION

[0004] A hand-held electric circular saw according to the disclosures of
the prior art usually had a rotatable protection guard, a circular saw
blade, an adjustment mechanism for cutting depth and an adjustment
mechanism for cutting angle. The cutting depth of the circular saw refers
to the distance that the circular saw blade protrudes to below the base
plate of the electric circular saw. The circular saw blade can pivot up
and down with respect to the base plate of the electric circular saw
around an axis parallel to the rotation axis, and can be locked at a
predetermined position with respect to the base plate by means of a clamp
device. The hand-held electric circular saw is usually supported by the
base plate that works on the workpiece directly, so as to facilitate
controlling of the vertical and inclined positions of the circular saw
blade with respect to the workpieces by users.

[0005] The prior hand-held electric circular saw with a protection guard
was primarily used for push-type cutting, and rarely used for insert-type
cutting. A circular saw without the protection guard is better designed
for insert-type cutting. Such a circular saw that can implement the
insert-type cutting has a saw blade that may pivot up and down in unison
with the housing of the motor or the gearbox with respect to the base
plate so as to adjust the cutting depth. To help with safety, the saw
blade of such an insert-type circular saw cannot be locked at a
predetermined position with respect to the base plate. However, the
movement may be limited to a specific area by a backstop. Likewise for
other safety reasons, a spring-like device may be mounted into the
insert-type circular saw for pressing the blade into the position of the
minimal cutting depth, instead of the protection guard. A circular saw
with this structure for implementing the insert-type cutting does not
require the clamp device for controlling the cutting depth of the prior
art implementations which would make the saw unsuitable for push-type
cutting operations.

SUMMARY OF THE INVENTION

[0006] The object of the present application is to provide a power tool
that can implement both push-type cutting and insert-type cutting
methods. To achieve this objective, the power tool of the present
application has a housing, a motor in the housing, a circular saw blade
driven to rotate by the motor about a rotation axis, and a base plate
that supports the housing and is positioned on the surface of the
workpiece to be cut. The housing may be connected to the base plate
pivotably around a pivotal axis that is parallel to the rotation axis.
The base plate may have an elongated slot for the circular saw blade to
protrude below the base plate. Such a power tool may have a first cutting
mode that may perform a cutting operation to a first predetermined depth
and a second cutting mode that may allow for vertical cutting in a
limited area.

[0007] The above described power tool may also have a switching device for
switching between the first cutting mode and the second cutting mode. As
a result, the power tool disclosed in the present application lends
itself to both a push-type cutting function and an insert-type cutting
function using the switching device to switch between the first cutting
mode and the second cutting mode. As a result of the two modes of
operation, operating efficiency is enhanced by integrating two functions
that are normally implemented by two different power tools into one power
tool.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] To understand the present application, it will now be described by
way of example, with reference to the accompanying drawings in which:

[0009] FIG. 1 is a perspective view of the power tool according to a first
embodiment of the present application;

[0010]FIG. 2 is a perspective view of the power tool of FIG. 1 with the
primary handle portion removed;

[0011]FIG. 3 is a side view of the power tool of FIG. 1 arranged for the
deepest cutting depth;

[0012]FIG. 4 is a side view of the power tool of FIG. 1 arranged for the
shallowest cutting depth;

[0013]FIG. 5 is a perspective view of the power tool of FIG. 1 with the
primary handle and the base plate removed;

[0014]FIG. 6 is a perspective view of the base plate and the depth guide
bracket of the power tool according to the present application;

[0015]FIG. 7A is a perspective view illustrating the insert-type cutting
arrangement of FIG. 1 with the first clutch disc and the second clutch
disc detached from each other;

[0016]FIG. 7B is a top plan view of the insert-type cutting arrangement
of FIG. 7A;

[0017]FIG. 7c is a cross sectional view of the insert-type cutting
arrangement taken along the line C-C in FIG. 7B;

[0018]FIG. 8 is a perspective view of the power tool of FIG. 1 with an
exploded view of the insert-type cutting arrangement;

[0019] FIG. 9 is a perspective view of the power tool of FIG. 1 with
another exploded view of the insert-type cutting arrangement;

[0020] FIG. 10 is a perspective view of the power tool of FIG. 1 arranged
to cut obliquely in the push-type cutting mode;

[0021] FIG. 11A is an exploded view of the insert-type cutting arrangement
according to another embodiment of the present application;

[0022] FIG. 11B is a side view of the insert-type cutting arrangement of
FIG. 11A;

[0023] FIG. 11C is a sectional view taken along the direction A-A in FIG.
11B;

[0024]FIG. 12 is a side view illustrating the power tool according to the
first embodiment of FIG. 1, wherein the lower guard may be opened
automatically;

[0025]FIG. 13 is a side view illustrating the power tool according to the
first embodiment of FIG. 1, wherein the primary handle has a first
handling position and a second handling position;

[0026]FIG. 14A is a bottom view illustrating the power tool according to
the first embodiment in FIG. 1, wherein the base plate has a guide groove
and roller device; and,

[0027]FIG. 14B is a side view illustrating the power tool according to
the first embodiment in FIG. 1, wherein the base plate has a guide groove
and roller device.

DETAILED DESCRIPTION

[0028] FIGS. 1 and 2 illustrate a power tool 10 according to a first
embodiment of the present application, which has a housing 11, a motor
(not shown) in the housing 11 and a circular saw blade 12 driven to
rotate by the motor. The circular saw blade 12 has a rotation axis 121
around which it can rotate. The circular saw blade 12 is covered in its
upper portion by a stationary guard 122 and in its lower portion by a
rotatable lower guard 123. An operating rod 124 is provided for moving
the lower guard 123 between a position at which the circular saw blade 12
is exposed and a position at which the circular saw blade 12 is covered.
The power tool 10 also comprises a base plate 13 which supports the
housing 11 mounted thereon and contacts the surface of the workpiece to
be cut. The housing 11 is pivotably coupled to the base plate 13 and may
pivot upward and downward around an axis 14 that is parallel to the
rotation axis 121. The base plate 13 is provided with an elongated slot
15, through which the circular saw blade 12 may protrude below the base
plate 13. The housing 11 may also pivot obliquely right and left around
an axis 16 that is perpendicular to the rotation axis 121. The angle that
the housing 11 pivots with respect to the base plate 13 may be determined
by an angle bracket 17 having a scale indication. After the housing 11
pivots into the predetermined angle position, a knob 18 is used to fix
the housing 11 in the predetermined angle position for implementing the
cutting at an inclined angle. Hand-held electric circular saws in the
prior art usually have such a function of inclined cutting. The
structures for achieving this function are also well known for the
persons skilled in the art. Therefore details are not described herein.
The power tool 10 also comprises a primary handle 19 and a secondary
handle 20 for holding by the users.

[0029] Referring to FIGS. 3-6, the power tool 10 also comprises a depth
guide bracket 40 which is mounted pivotally on the base plate 13 and may
pivot obliquely left and right together with the housing 11 around the
axis 16. The depth guide bracket 40 has a first elongated track 51 and a
second elongated track 61 thereon. The first track 51 and the second
track 61 constitute parts of two circles and have a common center. A
clamp device 52 is connected through the primary handle 19 to the
stationary guard 122 located on one side of the motor. However, in the
other embodiments, the clamp device 52 may also be directly connected to
the stationary guard located on one side of the motor. The clamp device
52 comprises a knob 521 and a bolt 522 partly positioned in the first
track 51. The bolt 522 is connected to the knob 521 at one end thereof
and has a head 523 connected fixedly to the stationary guard 122 at the
other end. When the stationary guard 122 together with the handle 19
pivots upward around the axis 14, the portion of the bolt 522 in the
first track 51 slides in the first track 51 correspondingly. The clamp
device 52 and the depth guide bracket 40 comprising the first track 51
commonly form an adjustment mechanism for the cutting depth, which may
lock the housing 11 in the position of a predetermined cutting depth with
respect to the base plate 13, so that a push-type cutting in this depth
position may be implemented. The stationary guard 122 located on one side
of the motor is marked with a cutting depth scale 22. The setting of the
cutting depth may be accomplished by aligning the mark 23 located on the
depth guide bracket 40 with the exact value located on the cutting depth
scale 22. The steps of setting the cutting depth are as follows: Firstly,
rotating the knob 521 to unlock the housing 11 from the depth guide
bracket 40, and then operating the primary handle 19 to pivot the housing
11 up and down around the axis 14, and the portion of the bolt 522 in the
first track 51 slides in and along the first track 51. Then, while
observing the scale, rotating the knob 521 in the reverse direction to
fixedly lock the housing 11 on the depth guide bracket 40 when the
housing 11 pivots into the position of a desired cutting depth, so that
the housing 11 is fixed at the position of the desired cutting depth with
respect to the base plate 13. The well-known hand-held electric circular
saws with protection guards usually have such an adjustment mechanism for
the cutting depth and their constructions are well known to the persons
skilled in the art, thereby details are not described herein. FIG. 3
illustrates the side view of the power tool in the state of the largest
cutting depth. FIG. 4 illustrates the side view of the power tool in the
state of the smallest cutting depth.

[0030] Compared with the well-known hand-held electric circular saw with a
protection guard, the power tool 10 also comprises a second track 61
likewise on the depth guide bracket 40 and a backstop 62 slidable in the
second track 61. The backstop may be comprised of a bolt. An operating
handle 63 is connected to the backstop 62. The depth guide bracket 40
comprising the second track 61, and the backstop 62 as well as the
operating handle 63 together constitute an adjustment mechanism for the
depth of the backstop, which allows the housing 11 to pivot up and down
in a limited depth area with respect to the base plate 13, so as to
implement the insert-type cutting. The depth guide bracket 40 is also
marked with depth indicating scale 24. The setting of the depth of the
backstop is accomplished by aligning the indicator 631 attached to the
backstop 63 with the value on the depth indicating scale 24. The steps of
setting the depth of the backstop are as follows: rotating the operating
handle 63 to unlock the backstop 62 from the second track 61; sliding the
backstop 62 to the desired depth position along the second track 61; and,
rotating the operating handle 63 in the reverse direction to lock the
backstop 62 in the second track 61. After following these steps, the
power tool 10 is in such a state that it may implement the insert-type
cutting, the power tool 10 may implement vertical insert-type cutting in
the depth area.

[0031] Persons skilled in the art may easily envisage that a depth guide
bracket comprising only one track may implement both the push-type
cutting and the vertical insert-type cutting functions, instead of the
above depth guide bracket 40 comprising the first track 51 and the second
track 61 simultaneously. For example, the second track 61 may be removed
and the backstop 62 may be arranged slideably in the first track 51. When
a push-type cutting is needed to be implemented, the backstop 62 is
positioned into the lowest position of the first track 51, and then the
clamp device 52 which is also positioned in the first track 51 is used to
fix the housing 11 at a position of the desired cutting depth with
respect to the base plate 13 to implement the push-type cutting. When an
insert-type cutting is needed, the clamp device 52 is used to unlock the
housing 11 from the base plate 13, and the operating handle 63 is used to
lock the backstop 62 at the position of a desired depth in the first
track 51, so as to allow the insert-type cutting function.

[0032] The power tool 10 also comprises an insert-type cutting device 70
which enables the circular saw blade 12 to cut vertically in a limited
depth area and is fixed to the base plate 13 by a bolt 71. A clutch
device 80 is coupled between the housing 11 and the insert-type cutting
device 70, by which the insert-type cutting device 70 can be connected to
or disconnected from the housing 11 so as to accomplish the switching
between the above insert-type cutting mode and the push-type cutting
mode.

[0033] Now referring to FIGS. 7-9, the clutch device 80 comprises a first
clutch disc 81 and a second clutch disc 82. The first clutch disc 81 is
connected to the housing 11 by a screw 83 and a pivotal shaft 84 that is
inserted and connected to the pivotal support 841 mounted on the base
plate. In other embodiments, the first clutch disc 81 may also be formed
on the housing 11 directly, while the second clutch disc 82 is connected
to the insert-type cutting device 70. The insert-type cutting device 70
comprises an outer housing 72 connected adjacent to the second clutch
disc 82, a shaft 73 for connecting the second clutch disc 82 and the
outer housing 72 together in series, and a spring 74 located in the
second clutch disc 82 and the outer housing 72. The second clutch disc 82
is connected to the outer housing 72 by the connecting rod 85 thereon for
limiting the position of the spring 74. One end of the shaft 73 away from
the second clutch disc 82 protrudes out of the outer housing 72 with a
knob 75 mounted on said end. Beside the knob 75, a through hole 76 is
formed on the shaft 73, and a locking pin 77 is fixedly inserted into the
through hole 76 with two ends protruding out of the through hole 76.

[0034] In order to implement the insert-type cutting, the insert-type
cutting device 70 needs to be connected to the housing 11. Firstly, the
power tool 10 shall be moved into the position of the minimal cutting
depth as shown in FIG. 4, where the first clutch disc 81 and the second
clutch disc 82 may be mated and aligned with each other. After the first
clutch disc 81 and the second clutch disc 82 are mated and aligned with
each other, the knob 75 is rotated to enable the locking pin 77 to be
aligned with the elongated slot 78 located on the housing 72 of the
insert-type cutting device. The knob 75 is pushed left to enable the
locking pin 77 to pass through the elongated slot 78. Finally, the knob
75 is rotated 90 degrees to lock the insert-type cutting device 70 and
the first clutch disc 81 together. Since the first clutch disc 81 and the
housing 11 are fixedly connected, the insert-type cutting device 70 is
fixedly connected to the housing 11. When the insert-type cutting device
70 is connected to the housing 11 by the first clutch disc 81 and the
second clutch disc 82, the power tool 10 is switched into the insert-type
cutting mode, where the users may implement an inset-type cutting. In
this insert-type cutting mode, the insert-type cutting device 70 is
connected to the housing 11, so the spring force of spring 74 in the
insert-type cutting device 70 acts on the housing 11. When a user presses
the power tool 10 down against the spring force of the spring 74, the saw
blade 12 is inserted into the workpiece to be cut. Correspondingly the
first clutch disc 81 pivots down about the pivotal shaft 84 and drives
the second clutch disc 82 engaged together with itself to rotate in
clockwise direction, while the housing 72 of the insert-type cutting
device 70 is stationary. When the power tool 10 is moved down and comes
into contact with the backstop 62, the user stops applying the force
downwardly. The power tool 10 is restored back to the position of the
initial cutting depth automatically by the spring 74 arranged in the
second clutch disc 82 and the insert-type cutting device 70. In this
embodiment, the position of the initial cutting depth is the position of
the minimal cutting depth as shown in FIG. 4. After setting a position of
the backstop depth by the above adjustment mechanism for the backstop
depth, a user may implement the vertical insert-type cutting repeatedly
in the depth area between the position of the minimal cutting depth and
the backstop 62. Persons skilled in the art may easily envisage that the
first clutch disc 81 and the second clutch disc 82 may be engaged and
aligned with each other in other selected positions without limitation to
the position of the minimal cutting depth, such as the position of the
deepest cutting depth as shown in FIG. 3 or other positions between the
deepest cutting depth position and the minimal cutting depth position.

[0035] By reversing the above steps of locking, the insert-type cutting
device 70 may be disconnected from the housing 11. Firstly, the knob 75
is rotated by 90 degrees to enable the alignment of the locking pin 77
with the elongated slot 78, and the knob 75 is pulled rightward to drive
the shaft 73 to move rightward correspondingly and further to drive the
locking pin 77 out of the elongated slot 78. Then the acting force
applied on the first clutch disc 81 and the second clutch disc 82
disappears, so the first clutch disc 81 and the second clutch disc 82 are
disengaged so as to disconnect the insert-type cutting device 70 from the
housing 11. When the insert-type cutting device 70 and the housing 11 are
in the disconnected state, the knob 75 is rotated so that the locking pin
77 is not aligned with the slot 78 but abuts against the outer end
surface 79 of the housing 72 of the insert-type cutting device 70, so as
to effectively prevent the accidental engagement of the first clutch disc
81 and the second clutch disc 82.

[0036] When the insert-type cutting device 70 is disconnected from the
housing 11, the power tool 10 is switched into the push-type cutting
mode, in which the spring force of the spring 74 doesn't act on the
housing 11. After setting a position of a certain cutting depth by means
of the above adjustment mechanism for cutting depth, a user could
implement the push-type cutting in this cutting depth. In this invention,
the above inclined cutting function could only be implemented in the
push-type cutting mode. Specifically, the insert-type cutting device 70
is disconnected from the housing 11 so that a gap is generated around the
first clutch disc 81 (see FIG. 10). After the knob 18 is unlocked and the
power tool 10 is pivoted to a predetermined angle position, the knob 18
is locked so as to fix the power tool 10 at the predetermined angle
position for implementation of the inclined cutting.

[0037] In the present application, the stationary guard 122 covering the
upper portion of the circular saw blade 12 may be directly formed on the
housing 11 or as a part of the housing 11. It may also be fixedly
connected to the housing 11 as a separate member. When the stationary
guard 122 covers the upper portion of the circular saw blade 12 as a
separate member, the insert-type cutting device 70 is fixedly connected
to the stationary guard 122 by the clutch device 80.

[0038] Persons skilled in the art may also envisage that the insert-type
cutting device 70 may be not limited to be mounted on the base plate 13,
either. The insert-type cutting device 70 and the second clutch disc 82
may be mounted or directly formed on the housing 11, and the first clutch
disc 81 may be fixedly mounted on the base plate 13, such that the power
tool will be switched into the insert-type cutting mode after the first
clutch disc 81 and the second clutch disc 82 are aligned with each other
and locked together.

[0039] FIGS. 11A-C illustrate another embodiment of the insert-type
cutting device according to the present application. This insert-type
cutting device 70' comprises an outer housing 72' which may be connected
adjacent to the second clutch disc 82, a bolt 73' and a nut 100 for
fixedly connecting the second clutch disc 82 and the outer housing 72'
together, and a spring 74' located in the second clutch disc 82 and the
outer housing 72'. A backstop bolt 85' may be mounted through the second
clutch disc 82 and the outer housing 72' on the indicator panel 101 for
limiting the positions of the spring 74'. The base plate 13 comprises an
elongated slot 104 in which the insert-type cutting device 70' may be
mounted. After the insert-type cutting device 70' may be disposed into
the slot 104 from above of the base plate 13 and a base cover 102 may be
fixed from below the base plate 13 to the lower portion of the
insert-type cutting device 70' by a screw 103, the two long sides of the
elongated slot 104 in the direction perpendicular to the saw blade are
just clamped in the gap formed between the base guard 102 and the
insert-type cutting device 70', such that the insert-type cutting device
70' may be mounted on the base plate 13. The insert-type cutting device
70' may be limited for the displacement in the direction perpendicular to
the bottom plate 13, but it may still displace in the direction parallel
to the two long sides of the elongated slot 104. A groove 105 may be
formed between the lower end of the insert-type cutting device 70' and
the base cover 102, and a spring 106 may be placed between the groove 105
and the projection 107 on the base plate 13. A screw cap 77' may be
mounted on the end surface 79' of the insert-type cutting device 70'. For
cooperation with the insert-type cutting device 70', a pressing device
200 may be also provided in this embodiment for pressing the first clutch
disc 81 and the second clutch disc 82 which are aligned with each other
together. The pressing device 200 comprises a locking support 201, a
locking pin 202 inserted into the locking support 201, a locking screw
203 through the locking support 201 for pressing the locking pin 202, and
a locking handle 204 mounted on the locking pin 202 and rotatable around
the locking pin 202. One end 205 of the locking handle 204 may be
operated directly by the hands of the users, and the other end 206 has a
cam surface in contact with the screw cap 77' mounted on the end surface
79' of the insert-type cutting device 70'. The pressing device 200 may be
mounted into the elongated slot 104 from above the base plate 13, and
then a locking support cover 207 may be fixed from below the base plate
13 on the lower surface of the pressing device 200 by a screw 208, such
that the pressing device 200 may be fixedly mounted into the slot 104 of
the base plate 13. The locking handle 204 may be rotated by its one end
205. When the cam surface of a larger radius of the other end 206 comes
into contact with the screw cap 77', the second clutch disc 82 and the
insert-type cutting device 70' are moved together towards the first
clutch disc 81. The second clutch disc 82 and the first clutch disc 81
are pressed and connected together so as to fixedly connect the
insert-type cutting device 70' onto the housing. When the cam surface of
a smaller radius of the other end 26 comes into contact with the screw
cap 77', the spring force of the spring 106 forces the second clutch disc
82 and the insert-type cutting device 70' to move together in the
direction away from the first clutch disc 81. The first clutch disc 81
and the second clutch disc 82 are separated so as to disconnect the
insert-type cutting device 70' from the housing. By means of such a
locking handle 204 having cam surfaces, the connection or the
disconnection between the insert-type cutting device and the power tool
can be accomplished quickly. The operation is more comfortable and
convenient in comparison with the above method of knob locking.

[0040] A person skilled in the art may also envisage some other locking
devices to accomplish the connection or the disconnection of the
insert-type cutting device to or from the housing. Moreover, the locking
device is not limited to the mechanical structures, and may also be some
other devices achieving the locking function by magnetic force.

[0041] Referring to FIG. 12, the power tool 10 in the above embodiments
may also be added with a linkage mechanism 90 for automatically opening
the lower guard 123 in the insert-type cutting mode. The lower guard 123
may be pivotably mounted on the shaft 125 of the saw blade 12. One end 91
of the linkage mechanism 90 may be connected to the lower guard 123, and
the other end 92 may be connected to the pivotal support 841. When the
housing 11 and the circular saw blade 12 pivot downward around the
pivotal shaft 84 together, the lower guard 123 may be pulled to rotate in
the contrary direction by the linkage mechanism 90, so as to accomplish
the automatic opening of the lower guard 123. Preferably, persons skilled
in the art may also envisage that the linkage mechanism 90 may be
associated with the insert-type cutting device 70 by a linkage device.
When in the insert-type cutting mode, the insert-type cutting device 70
may be connected to the housing 11, and the lower guard 123 may be pulled
by the linkage mechanism 90 to accomplish the automatic opening of the
lower guard 123. When in the push-type cutting mode, the insert-type
cutting device 70 may be disconnected from the housing 11, such that the
linkage mechanism 90 doesn't act on the lower guard 123, so the lower
guard cannot be opened automatically.

[0042] Referring to FIG. 13, distinguishing the structure of the primary
handle 19 of the power tool 10 from the above embodiments, the primary
handle 19' comprises a first handling portion 191 and a second handling
portion 192. The user may select different handling portions according to
different cutting modes so as to make the operation more comfortable.
Certainly, persons skilled in the art may also envisage that a rotatable
handle may be arranged on the housing. Thus users may select to set the
handle in different positions as needed for implementing the cutting
operation.

[0043] Referring to FIGS. 14A-B, a guide groove 95 may be added on the
base plate 13 of the power tool 10 in the above embodiments. The cutting
straightness of the power tool will be advantageously enhanced by the
cooperation of the guide groove 95 and the guiding device. Persons
skilled in the art may also envisage that a pulley device 96 may be added
on the base plate 13 so as to facilitate the pushing forward of the power
tool 10 in the insert-type cutting mode.

[0044] The embodiments described above are only explanatory for the
concepts and principles of the invention without limitation to the
contents of the invention. Various changes and modifications of the
embodiments that should be considered within the scope of the present
application will occur to a person skilled in the art.